Asymmetric aspheric contact lens

ABSTRACT

A contact lens for use on a patient&#39;s eye with an asymmetric aspheric cornea, the lens having an anterior surface, a posterior surface and a base, the posterior surface having a peripheral portion which is asymmetric and aspherical and at least coextensive with the base of the lens. The peripheral portion asymmetrically and aspherically matching a corresponding peripheral portion of the cornea which lies under the peripheral portion of the lens when the lens is worn in the patient&#39;s eye. The contact lens is not substantially greater in diameter than said cornea. The process for manufacturing the lens uses three-dimensional topographic data (including elevation data) from a multiplicity of points on the cornea. The data is used to shape at least the peripheral portion of the posterior surface of the lens to cause it to conform to and/or match the corresponding surface of the cornea.

This is a continuation-in-part of U.S. application Ser. No. 08/119,351filed Sep. 9, 1993 now U.S. Pat. No. 5,502,518.

FIELD OF THE INVENTION

The present invention relates generally to contact lenses and to methodsof manufacture of contact lenses, and in particular to asymmetric,aspheric individually fitted contact lenses and methods of manufacturethereof.

BACKGROUND OF THE INVENTION

Thirty to forty percent of the human population under age 40 develop anocular refractive error requiring correction by glasses, contact lenses,or surgical means. Refractive errors result when the primary opticalelements of the eye, the cornea and the lens, fail to image incominglight directly on the retina. If the image is focused in front of theretina, myopia (nearsightedness) exists. If the eye image is focusedbehind the retina, hyperopia (farsightedness) exists. The focusing powerof the eye or any refracting medium is measured in units calleddiopters.

Approximately 20% of the patients under 40 having vision defects cannotwear contact lenses because the contact lenses do not fit (becomedislodged and/or are very uncomfortable), or they fail to provide therequisite optical correction, or both. In addition, many patients whocurrently wear contact lenses are not satisfied with the length of timethey can wear their lenses and/or with the visual acuity their contactlenses provide.

Over age 40, the percentage of the population requiring visioncorrection dramatically increases and the problems encountered withexisting contact lenses become much more common and acute.

Standard contact lenses are rotationally symmetrical and spherical. Thehuman cornea, however, is an "asymmetrically aspheric" surface.

"Aspheric" means that the radius of curvature along a corneal "meridian"(which is an imaginary line on the corneal surface passing through thegeometric center of the cornea, analogous to a geographic meridian) isnot a constant. Indeed, the corneal curvature flattens progressivelyfrom the geometric center to the periphery. "Asymmetric" means that theprofile of the corneal curvature along a half-meridian is not the sameas (i.e., it is not a mirror image of) the other half of the samemeridian. The degree to which corneas are aspheric and/or asymmetricalvaries from patient to patient.

Spherical lenses do not match the corneal curvature and geometry, andtherefore do not fit properly. The more irregular the patient's corneathe worse the fit, such that about 20% of the patients under age 40 areunable to wear standard contact lenses.

Standard contact lenses are rotationally symmetrical. The contact lensdesigner/fitter routinely combines a multiplicity of spheres or addsaspheric curves in conventional contact lens design. Sometimes thefitter will generate toric, bitoric and like surfaces in his efforts tofit lenses to the cornea. These more complicated lens designs remaininherently rotationally symmetric, i.e., the surfaces are generatedabout a central point of revolution. Toric lenses are currently made inone of two ways. The first and most common method is to crimp and thusdistort the lens blank before placing it in the lathe. After the crimpedlens is cut, it is allowed to spring open. The second method is to makethe toric lens directly on a lathe.

Because the human cornea has an asymmetrically aspheric surface, purelyspherical lenses poorly match the corneal curvature and geometry. Whenthe lens is designed as a hybrid of spherical and aspherical curves, theresultant lens surfaces are still rotationally symmetrical (i.e., theselenses are not asymmetrical and aspheric).

In an effort to alleviate these problems, manufacturers developed lenseswith varying curvatures on their posterior surface. For example, U.S.Pat. No. 5,114,628 discloses aspherical contact lenses made usingcorneal topographic data to control a lathe. (The data provideinformation on the slope of the corneal surface at different points onthe cornea but are based on measurements in two dimensions interpretedthree-dimensionally.) The resultant lens is aspherical (in both theanterior and posterior surface) but inherently symmetrical. Such a lensmay fit some patients better than the standard spherical lenses. Butother patients may experience more discomfort than with the sphericallenses. Thus, this type of aspherical symmetric lens does not provide asubstantial improvement in the number of patients that can comfortablywear contact lenses and/or wear contact lenses that provide them withthe requisite visual acuity.

Other U.S. patents (e.g., U.S. Pat. Nos. 4,923,467, 5,104,408 and5,156,622) disclose the shaping of a lenticule which is implanted withinthe substance of the cornea. These lenticules are not contact lenses.The lenticules described in these patents are shaped based on cornealtopographic mapping data. A laser is used to ablate material from a lensblank. However, the fit problems encountered with these implants are notthe same as those encountered with contact lenses. For example, unlike acontact lens, implanted lenticules are stationary and once installed inthe corneal stroma they neither "rock" on the cornea nor float on a tearfilm and are not subject to external forces such as eyelid pressure orthe force of gravity.

U.S. Pat. No. 2,264,080 to Hunter discloses a system for manufacturing a"contoured" scleral contact lens, i.e., a lens resting on the sclera,not on the cornea. Hunter teaches the creation of a mold of the surfaceof the eye which is then used as a "template" to mechanically radiallyguide a grinder over the surface of a lens blank. The grinder receivesinformation about the meridional topography of the mold and travels overthe surface of the lens blank in a back-and-forth fashion alongmeridians of the lens. Hunter's scleral lens intentionally hassufficient clearance from the cornea to avoid any contact with thesurface of the cornea. Moreover, his method of manufacture causes"ridges" or "cusps" to be formed on the posterior surface of the lens,which if present on a contact lens closely fitted to the cornea wouldcause discomfort to the wearer. Additionally, these ridges would bepresent in the optical field portion of a contact lens, obstructing thepatient's field of vision and thereby rendering the contact lensuseless.

The need in the art for better fitting contact lenses is illustrated inan article in Ophthalmology Times Nov. 1, 1992, p. 82, which disclosesthat future areas of research will involve increasingly sophisticatedaspheric optics and refinements on contact lenses based on theasphericity of the cornea.

In other words, although both the asphericity and asymmetry of thecornea may have been recognized in the art, only the asphericity of thecornea has been taken into account in contact lens design. The presentinventor unexpectedly discovered, that if part of the contact lensaccurately mimics the surface of the cornea in both asphericity andasymmetry, a better fit and/or a better vision correction can beachieved consistently. Thus, there is a need in the art for a contactlens that will decrease or eliminate the number of patients of all ageswho currently cannot wear contact lenses, and provide better comfortand/or visual acuity (including better correction of astigmatism) forpatients who now wear contact lenses.

OBJECTS OF THE INVENTION

It is therefore one object of the present invention to provide a contactlens with a more accurate vision correction and/or a more comfortablefit to the patient's cornea.

It is another object of the invention to rapidly and economicallymanufacture custom fit contact lenses, which are either spherical oraspherical, but are inherently asymmetric.

SUMMARY OF THE INVENTION

One aspect of the invention is directed to a contact lens for use on apatient's eye with an asymmetric aspheric cornea, said lens having: ananterior surface, a posterior surface and a base, said posterior surfacecomprising a peripheral portion, which is asymmetric and aspherical andat least coextensive with the base of said lens;

said peripheral portion asymmetrically and aspherically matching acorresponding peripheral portion of the cornea which lies under saidperipheral portion of the lens when the lens is worn in the patient'seye; and

said contact lens is no greater in diameter than said cornea.

More specific embodiments include without limitation one or more of thefollowing variations:

(a) the entire posterior surface asymmetrically and asphericallycorresponds to the surface of the cornea;

(b) the anterior surface of the lens may also be asymmetric andaspherical in whole or in part;

(c) at least part of the peripheral portion of the posterior surface ofthe lens has asphericity and asymmetry in a predetermined proportionallydivergent relationship with the corneal surface;

(d) the central portion of the posterior surface of the lens isspherical; and/or

(e) the peripheral edge portion of the lens has a variable thickness topermit for variations in symmetry and sphericity of the cornea whilemaintaining a conventional anterior edge and surface design.

In another aspect, the present invention provides a process formanufacturing the lens using three-dimensional topographic data(including elevation data) from a multiplicity of points on said corneaand using said data to guide the generation of at least the peripheralportion of the posterior surface of said lens to cause it to conform toand/or match the corresponding surface of said cornea.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will be more fullyunderstood from the following description of preferred embodiments withreference being made to the drawings in which:

FIG. 1a is a cross-sectional view of a spherical cornea fitted with aprior art spherical lens.

FIG. 1b is a cross-sectional view of a simple aspherical cornea fittedwith a prior art spherical lens.

FIG. 1c is a plan view of the simple aspherical cornea of FIG. 1b.

FIG. 1d is a cross-sectional view of a simple aspherical cornea fittedwith a prior art simple aspherical lens.

FIG. 1e is a cross-sectional view of an asymmetric aspherical corneafitted with a prior art simple aspherical lens.

FIG. 2 is a cross-sectional view of an asymmetric aspherical corneafitted with an asymmetric aspherical lens according to the presentinvention.

FIG. 3 is an enlarged cross-sectional view of the asymmetric asphericallens of FIG. 2.

FIG. 4 is a cross-sectional view of an asymmetric aspherical corneafitted with a combination spherical and asymmetric aspherical lensaccording to the present invention.

FIG. 5 is a plan view of the combination spherical and asymmetricaspherical lens of FIG. 4 fitted to a cornea.

FIG. 6 depicts the overall system and data flow for a lens manufacturingprocess according to the present invention.

FIG. 7 is a milling system for use in manufacturing a contact lensaccording to the present invention.

FIG. 8 is a partial cross-sectional view of an asymmetric asphericalcornea fitted with a combination spherical and asymmetric asphericallens according to the invention in which a portion of the asymmetricaspherical posterior surface does not match the corneal surface butconforms to said surface in a proportionally divergent relationship.

FIG. 9 is a sectional view taken along line 9--9 of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following terms are assigned the meanings described below:

(a) "Match" applied to corneal and lens surfaces means "fit essentiallyexactly". Thus, if a contact lens surface or portion "matches" thecorresponding portion of the corneal surface, the three-dimensionaltopography of the lens surface or portion is essentially (or evenexactly) superimposable on the three-dimensional topography of thecorresponding corneal surface portion (generally, the more measurementsof the corneal topography which are taken, the more exact the match).

(b) "Conform" applied to corneal and lens surfaces (or portions) isbroader than "match". Thus, a surface portion of a lens "conforms" to acorresponding surface portion of the cornea if their three-dimensionaltopographies are not superimposable but the topography of every point onthe lens surface is derived from a topography superimposable on thecorneal surface by operation of a simple mathematical relationship. Forexample, a lens surface portion "conforms" to a corresponding cornealsurface portion by a radially "proportionally divergent" relationship ifthe two surface portions have a "matching" boundary (i.e., a matchingcontour line) at the periphery but progressively diverge from oneanother in a radially inward direction. See, e.g., Zone 101 of cornea10" and the same zone 101 of lens 60' in FIG. 8.

In order to appreciate the unique features and advantages of the contactlens and method of manufacture of the present invention, it is helpfulto understand the structure of the cornea and the interaction of thecornea with the prior art contact lenses. FIGS. 1a through 1d illustratevarious prior art contact lenses fitted to variously shaped hypotheticalcorneas. The depictions in these Figures are not to scale and certainstructures have been exaggerated for illustrative purposes. Each of thecross sections of the eye depicted in FIGS. 1a-1d have been taken acrossa single meridian of the eye.

FIG. 1a depicts a cross section of a hypothetical spherical cornea 10which has been fitted with a spherical contact lens 30 of the prior art.(This illustration does not have any clinical basis since no humancornea is perfectly spherical.) In this Figure, it can be seen that ifthe human eye were perfectly spherical it could be easily fitted with aspherical lens 30. In a spherical lens, the radius of curvature at anypoint on the surface of the lens is equal to the radius of curvature atany other point on the same surface of the lens. Moreover, a sphere isinherently symmetric.

The optical correction achieved by a contact lens is, inter alia, afunction of the power of the lens. In turn, the power of a lens is,inter alia, a function of the index of refraction of the material usedfor the lens and the algebraic difference between the curvature of theanterior (outer) surface 32 of the lens and the curvature of theposterior (inner) surface 34 of the lens. (For additional details onconsiderations that may be taken into account for achieving a givenoptical correction, see, e.g., U.S. Pat. No. 5,114,628, incorporatedentirely by reference.)

Also seen in this FIG. 1a are other anatomical features of the eyeincluding the sclera 15, the iris 20 and the pupil 25. The pupil 25 isthe opening formed by the iris 20. As more light is required to enterthe eye in order to form an image, the iris 20 opens and the diameter ofthe pupil grows larger. The lens 30 depicted in FIG. 1a covers at mostthe entire cornea 10, and has a diameter of up to approximately 10millimeters. Some lenses of the prior art (not shown) have a much largerdiameter and extend to cover part of the sclera 15, but the presentinvention concerns contact lenses that do not extend substantially pastthe edge of the cornea.

FIG. 1b is a cross-sectional view of a hypothetical symmetric asphericalcornea 10' fitted with the prior art spherical lens 30 of FIG. 1a.Geometric centerline H is an axis which is normal to the Iris Plane andpasses through the geometric center of cornea 10'. In an asphericalcornea, such as the cornea 10' depicted in this Figure, the radius ofcurvature is not constant along any meridian, e.g. , from a point on thegeometric centerline H to either of its edges 12 or 13. For example, theradius of curvature at point A on the cornea 10' is different from theradius of curvature of the cornea 10' at point F. The radii of curvaturedepicted in FIG. 1b have been exaggerated in order to illustrate theasphericity of cornea 10'. It can be thus appreciated that a sphericallens 30 does not fit well nor rest stably on a symmetric asphericalcornea 10'. There will always be significant "gaps" (i.e., areas ofnonconformity) between the posterior surface 34 of the lens 30 and theanterior surface 11 of the cornea 10'. Because of these gaps, there willbe undesirable movement and "rocking" of the lens 30 on the corneawhich, depending on the degree of movement/rocking, will render the lens30 uncomfortable and/or ineffective in correcting vision.

The term "symmetric", defined above, has been used to describe thenature of the shape of the aspherical cornea 10'. A feature of thesymmetric cornea is that the radius of curvature at a point located at agiven radial distance from the geometric centerline H, is the same asthe radius of curvature at any other point located at the same radialdistance from the centerline H. FIG. 1c in conjunction with 1billustrates this feature. FIG. 1c is a plan view of the symmetricaspherical cornea 10' of FIG. 1b. Points A and B both reside on theanterior surface 11 of cornea 10' along the same meridian M1. Points Aand B are both at a radial distance C from the geometric centerline H ofcornea 10', each in a different direction along meridian M1 fromgeometric centerline H. Points D and E reside along meridian M2 which isangularly displaced 90 degrees from meridian Mi. Points D and E are alsoeach a radial distance C from geometric centerline H. In a symmetricaspheric cornea, the radius of curvature is the same at points A, B, Dand E, all radially equidistant from centerline H. Any two halves of thecornea 10' are mirror images of each other taken along any meridian(e.g., M1, M2 or any other meridian).

FIG. 1d illustrates a cross section taken across a meridian of thesymmetric aspherical cornea 10' fitted with a prior art symmetricaspherical lens 40 (which can be manufactured by conventional lathingtechniques). As can be seen in this Figure, the curvature of theposterior surface of lens 40 has been constructed to conform to thecurvature of the cornea 10'. As compared with the spherical lens of FIG.1b, the aspherical lens 40 of this Figure provides a better fit for theaspherical symmetrical cornea of FIG. 1d which would result in improvedcomfort and vision. However, symmetric aspherical lenses, which have thesame meridian cross-sectional shape throughout, whose shape correspondsto the patient's average corneal asphericity, still leave a sizablepercentage of the patient population unable to wear them comfortably orsee well enough through them.

FIG. 1d also is useful in explaining the deficiencies of a symmetricaspheric lens 40 when worn on an asymmetric aspheric cornea. Q and R arepoints on the posterior surface 44 of lens 40 along a particularmeridian. Points Q and R are both at the same radial distance C from thegeometric centerline H of cornea 40. In a symmetric aspheric lens 40fitted to a symmetric aspheric cornea, points Q and R are the samedistance (S), away from a plane P. Plane P is a reference plane which isparallel to the Iris Plane. Centerline H is normal to reference plane P.All points on the lens 40 located at a radial distance C from geometriccenterline H will be a distance V away from plane P. In other words thesame geometry described above with respect to the symmetric asphericcornea 10 is present on the symmetric aspheric lens 40. Therefore,points Q and R on the lens 40 will perfectly match points A and B on thecornea 10'. Indeed, the entire posterior surface of the lens depicted inFIG. 1 d will match the corresponding surface of the cornea 10' whichthe lens 40 covers. This is to say that no gaps exist between points Qand A or points R and B. A uniform narrow space exists between theposterior surface 44 of lens 40 and the anterior surface 11 of cornea10'. In actual practice, this uniform capillary space would be occupiedby a tear film. Tear flow and tear exchange through this space isinfluenced by the capillary effect.

In FIG. 1d the lens is depicted positioned on the cornea such that thegeometric centerline H of the cornea 10' coincides with the geometriccenterline of the lens 40 and a single centerline H has been depicted torepresent both geometric centerlines in this Figure and those whichfollow.

Unfortunately, a patient's cornea is highly unlikely to be symmetricallyaspheric, as depicted in FIGS. 1b-1d. By far, the typical patient has acornea which is both asymmetric and aspherical such as cornea 10"illustrated in FIG. 1e. FIG. 1e depicts the asymmetric aspheric cornea10" fitted with the prior art symmetric aspheric lens 40 of FIG. 1d. Asexpected, the symmetric aspheric lens 40 does not match the asymmetricaspheric cornea 10" as well as it fits the symmetric aspheric cornea 10'of FIG. 1d.

Both points A' and B' in FIG. 1e lie along the same meridian of thecornea 10" at the same radial distance C away from geometric centerlineH. Because of the asphericity of cornea 10", points A' and B' reside atdifferent elevations from the Iris Plane. The difference in elevationbetween points A' and B' is shown as distance G. The elevationaldifference G between two points on the same meridian will render exactfitting of a symmetrical aspheric contact lens 40 on a asymmetricalaspheric cornea 10" impossible.

As seen in FIG. 1e, there exists a significant gap 45 between point A'on the anterior surface 11' of cornea 10" and the corresponding point Qon the posterior surface 44 of lens 40. When manufacturing thesymmetrical lens 40, sufficient material is removed from the lens blanksuch that the lens will clear the highest elevation point at a givenradius. In the particular example depicted in FIG. 1e, lens blankmaterial has been removed at point R so that the lens 40 will notimpinge on the cornea at point B'. Because the lens is symmetrical,point Q on lens 40 is at the same elevation as point R and it willtherefore not match (elevationally) point A' on the cornea, and gap 45results. The location, relative size, shape and number of gaps such as45 determines whether it will be feasible to fit a patient with asymmetric aspheric contact lens such as lens 40 and whether, iffeasible, the fit will be satisfactory. If a gap occurs at the marginaledge 47 (or base) of lens 40, which is the portion of lens 40 resting onthe cornea, such as gap 46, the lens will tend to "rock" along themeridian containing the gap (or will rest on the cornea in a position atwhich the lens 40 and the cornea 10" will be optically misaligned). Witha symmetrical lens such as lens 40, it is inevitable that gaps such asgap 46 will occur around the marginal edge 47 because of elevationaldifferences in the corneal surface where the marginal edge 47 meets thecornea. Furthermore, because of gap 46, there are potential problemswith the eyelid catching the marginal edge 47 and displacing the lens40. The marginal edge 47 will appear to be raised from the surface ofthe cornea 11' due to gap 46 between the surface 11' and the lens 40. Afurther problem with gaps such as gap 45 (which are not created bydesign but by the failure of the design and method to account forcertain features of the cornea) is the uncontrolled pooling of the tearfilm between the cornea and the posterior surface of the lens. If tearpooling is excessive, the lens may be so uncomfortable so as to make itvirtually impossible for a patient to wear. Similarly, if the lensphysically touches the central cornea, the corneal physiology will be sointerrupted as to induce the cornea into an oxygen poor state which willbecome immediately apparent to the patient. If such an intolerablesituation were to occur, the lens must be immediately removed from theeye.

FIG. 2 illustrates a cross section of the asymmetric aspherical cornea10" fitted with an asymmetric aspherical contact lens 50 to illustrateone aspect of the present invention. The anterior surface of asymmetricaspherical lens 50 is manufactured to conform precisely to (i.e., tomatch) the geometry of the asymmetric astigmatic cornea 10". The lens 50is shown in greater detail in FIG. 3. As seen in FIG. 3, the lens 50 ofthe present invention has been made such that the posterior surface 54of the lens 50 matches the asymmetric aspheric geometry of the anteriorsurface 11 of cornea 10". In practice, the center area (optical zone)will not match the cornea and only the periphery will match the cornea,as will be described below.

Points S and T in FIG. 3 lie along the same meridian on the posteriorsurface 54 of lens 50, and are both at the same radial distance C fromthe geometric centerline H of lens 50. Geometric centerline H is normalto reference plane P. Since the posterior surface 54 of the lens 50 hasbeen made to match the irregular, asymmetric, asphericity of cornea 10",points S and T (equidistant from centerline H) reside at differentelevations with respect to reference plane P. Point T is at a distanceZ1 from plane P while point S is at a distance Z2 from plane P. Becauseof the asymmetry of lens 50, distance Z2 is greater than distance Z1,the difference being G. Assuming that the cross section of lens 50depicted in FIG. 3 is taken along the same meridian as the cross sectionof cornea 10" in FIGS. 1e and 2, point S on lens 50 corresponds to pointA' on the cornea 10" and point T on lens 50 corresponds to point B' oncornea 10", since all four points are the same radial distance C fromgeometric centerline H of the lens 50 and the cornea 10".

The geometry of posterior surface 54 of lens 50 has been made to conformto the topography of anterior surface 11" of cornea 10", and thereforethe elevational difference G between points S and T on the lens 50 isthe same as the elevational difference G between points A' and B' on thecornea 10". In comparison to the symmetric aspheric lens 40 depicted inFIG. 1e, the asymmetric aspheric lens 50 will not have any significantgaps between it and the cornea 10", such as gaps 45 and 46 in FIG. 1e.The thin uniform apparent gap depicted between posterior surface 54 oflens 50 and anterior surface 11" of cornea 10" (FIG. 2) is merely toshow that, in practice, the posterior surface of lens 50 will beseparated from cornea 10" by a thin tear film.

The anterior surface 52 of lens 50 is also shaped to be both asphericaland asymmetric so that, in conjunction with the posterior surface, itwill achieve the proper optical correction required by the patient. Asappreciated by one skilled in the art, the optical correction achievedby a contact lens is in part a function of the index of refraction ofthe material used for the lens and the algebraic difference between thecurvature of the anterior surface 52 and the curvature of the posteriorsurface 54 of lens 50. The anterior surface 52 will be asymmetricallyaspheric and will have a shape that will have a predeterminedrelationship to posterior surface 54 depending on the optical correctionrequired (this feature is not shown in FIGS. 2 or 3). This relationshipis determined by taking into account various optical considerationswhich are within the skill in the art. For examples of contact lensesusing aspheric optics and further discussion thereof, see U.S. Pat. Nos.5,019,098, 4,861,152 and 4,640,595.

A preferred embodiment of a contact lens according to the presentinvention is illustrated in FIGS. 4 and 5. Lens 60 depicted in theseFigures is a combination lens having a spherical central portion 66 andan asymmetric aspherical peripheral or rim portion 69. The peripheralportion 69 includes the base 70 of lens 60 and extends to the base curve65 of spherical portion 66. The geometry of central portion 66 of lens60 is intentionally chosen to be spherical because spherical optics arerelatively simple and achieve the best sight correction. The peripheralportion 69 of posterior surface 64 of lens 60 is shaped according to thecorneal topographic data to create an asymmetrically aspheric surfacewhich matches the topology (both in curvature and elevation) of anteriorsurface 11' of cornea 10". The peripheral portion 69 forms the bearingsurface upon which lens 60 rests on the cornea 10".

The average maximum physiological dilation of the human pupil (25) isapproximately four to five (4-5) millimeters. In a preferred embodimentof the present invention, central spherical portion 66 will have a basediameter of at least six (6) millimeters in order to provide opticalconnection over the entire optical zone created by dilated pupil 25. Inthis preferred embodiment, the width of peripheral asymmetric asphericzone 69 will not likely exceed approximately one to two (1-2)millimeters. Although it is possible that peripheral portion 69 willhave a uniform width, this is not necessarily the case, as illustratedin FIGS. 4 and 5. The width of the peripheral portion 69 can vary fromlocation to location around the base of the lens. In such cases, thelens is not necessarily of a round shape or configuration. One factorwhich influences the width of the peripheral portion at a particularlocation is the steepness of the cornea at that particular location. Ifthe cornea is very steep along a particular meridian, the width of themarginal area 69 can be increased to provide a larger bearing surface asat point K of FIG. 5. A flatter portion of the cornea can beaccommodated with a narrower peripheral portion 69 and a correspondinglysmaller bearing surface as at point L. At the limit, and assuming thecorneal topography permits, the width of the peripheral portion 69 canbe coextensive with the base 70 of lens 60. In practice, the base willnot be a mathematical line but will have a small but finite width. Theupper limit of portion 69 along a particular meridian is determined bythe shape of the base curve 65 as described herein (and the existence,if any, of an intermediate zone as in FIG. 8). The lower limit, or edge,is determined not only by the topography of the cornea but also bytaking into account the properties of the material from which the lensis made, tear flow considerations, and lens/eyelid interactions. Inother words, the fine features of the meridian profile of lens 60 at thetip of base 70, wherein the posterior and anterior surfaces meet, willbe subject to these additional considerations. Such edge design and edgelift determination is within the skill of the art, however, and willrequire no more than routine experimentation.

In FIG. 5, zones 66 and 69 have been shown as delineated by a sharpline. In an actual contact lens manufactured according to the presentinvention, the transition between spherical zone 66 and asymmetricaspheric zone 69 will be blended (i.e. smooth without sharp edges whichmay cause discomfort). The steepness of the transition at this interfaceis also dependent upon the relative steepness of the patient's cornea. Acornea with a steeper curvature will result in a lens with a steepertransition zone between the central spherical portion 66 and theperipheral asymmetric aspheric zone 69.

As will be appreciated by one skilled in the art, the radius ofcurvature for spherical central portion 66 is determined by thedifference between the elevation of the apex of the cornea (the point onthe cornea most distal from the iris plane) and the elevation of thehighest point on the cornea at what will be boundary 65 between centralportion 66 and peripheral portion 69. To ensure clearance over theentire cornea 10", the highest point of the cornea underlying peripheralportion 69 (point K in the embodiment of FIG. 5) will also determine thehighest point of the transition between base curve 65 of the sphericalsection 66 of lens 60 and peripheral portion 69, subject to leaving theentire central (optical) zone with sufficient clearance from the cornea.The lowest point of the cornea along the base curve will determine thelowest point of the transition.

FIG. 8 depicts a variation of a preferred embodiment of the presentinvention. The three zones 100, 101 and 102 in combination make up theperipheral area 69 in FIGS. 4 and 5. Zone 103 in FIG. 8 corresponds tothe spherical central area 66 of FIGS. 4 and 5. As in the lens of FIGS.4 and 5, the posterior surface of lens 60' in zone 100 matches theasymmetric aspherical cornea 10" (partially shown) in this same zone100. Adjacent to zone 100 is an intermediate zone 101. The cornea 10"continues to remain asymmetrically aspherical. The portion of lens 60'in intermediate zone 101 is also asymmetrically aspherical, but does notmatch the corneal topography. The lens 60' in intermediate zone 101conforms to the corneal topography in a predetermined proportionallydivergent relationship. The amount by which the topography diverges fromthe true corneal topography will be determined by a simple algebraicformula such as: Z'=Z+(X-5)/2 where Z' is new Z elevation of the lens, Zis the elevation of the lens without the divergence and X is the Xcoordinate of the location of the particular point on the lens (the Xaxis is parallel to the page of FIG. 8). The purpose of the intermediatedivergent zone 101 on lens 60' is to control the flow of lachrymal fluidinto and out of the gap between the lens 60' and the cornea 10". Byincreasing the amount of divergence, the capillary effect will beincreased and therefore more fluid will flow tinder the 60'. Conversely,if the divergence is decreases (ultimately to the point where Z'=Z). theamount of fluid flow will decrease.

Zone 102 is a transition zone (not to scale) between the asphericasymmetric portion of lens 60' and the central spherical portion of lens60'. The purpose of the transition zone 102 is to provide a blendedcurve between the aspherical asymmetric portion (zones 100-102) and thespherical portion (zone 103)

FIG. 9 illustrates how the peripheral edge portion 69 of lens 60 has avariable thickness to permit for variations in an asymmetric asphericalcornea, while maintaining a conventional anterior edge and surfacedesign. As illustrated in FIG. 9, the left half of the lens correspondsto the thinnest edge due to the cornea being the steepest in this areaand the fight half corresponds to the thickest edge due to the corneabeing the flattest in this area. If the edge is thinner than apredetermined minimum required thickness for lens structural strength(to avoid breakage during manufacture, the present invention willautomatically compensate by providing additional thickness on the lens'anterior edge surface. This additional thickness provides for asufficient thickness such that the edge has the shape of a conventionalanterior edge. It should be noted that the anterior surface 52 of lens60 illustrated in FIG. 9 is spherical. However, at least the rim portion69 of the posterior surface 54 is asymmetrical and aspheric. Both theuncompensated edge 74 (shown in phantom) and the actual compensated edge72 are illustrated in FIG. 9.

A system for manufacturing the asymmetric aspheric contact lens of thepresent invention is illustrated in FIG. 6. The system includes aCorneal Image Capture System 610, an Elevation Analysis Program 620, aComputer Aided Design System 630, a Command Processor 640 and a LensShaping System 650. The Corneal Image Capture System 610 is used inconjunction with the Elevation Analysis Program 620 in order to generatea three dimensional topographic map of the cornea 600 of the patientwhich is to be fitted with a contact lens. For this purpose, both slope(contour-line) and elevation data are necessary.

The Computer Aided Design System 630 is used as an aid in editing ormodifying the corneal topographic data prior to sending the data to aLens Shaping System 650 via the Command Processor 640. The CommandProcessor 640 takes the topographic data describing the surface of thelens to be shaped, either directly from the Elevation Analysis Programor from the Computer Aided Design System 630, and generates a sequenceof commands/control signals required by the Lens Shaping System 650. TheLens Shaping System 650 accepts from the Command Processor 640, asequence of commands which describe the movements in three dimensions(X, Y, Z in any one of cartesian, radial or spherical coordinates) ofthe Lens Shaping System to shape the particular custom fit contact lens.

Each of the systems described in FIG. 6 can be constructed as separateunits, or certain of the systems can be combined and practiced on asingle processor. For example, the Computer Aided Design System 630 andthe Command Processor are both software applications which can be loadedand executed on a single Personal Computer (PC) such as an IBM™compatible PC. Since the two applications do not have to run at the sametime, a very advanced PC is not required, but preferably a computer witha 486 processor (or equivalent) is preferred for the math intensiveElevation Analysis Program. In one embodiment of the system of FIG. 6,the Corneal Image Capture System 610 and the Elevation Analysis Program620 are located at a first location, such as a physician's office, whilethe Computer Aided Design System 630, Command Processor 640 and a LensShaping System 650 are all located at a second location, such as amanufacturing site. The links 622 and 623 can be accomplished via atelecommunications link, such as a modem or RS232 port (not pictured inFIG. 6) or merely by the passage of a diskette between the two systems.The Corneal Image Capture System 610 captures a two-dimensional image ofthe surface of the patient's cornea 600. System 610 captures the cornealimage by projecting an illuminating pattern onto the surface of thecornea 600 and captures the light reflected off the corneal surface.Traditional methods of illuminating the cornea 600 involve projecting aseries of calibrated concentric rings or mires such as described in U.S.Pat. No. 4,863,260. Although this patent describes one method ofobtaining corneal topographic data, several topographic systems (citedbelow) might use different methods. Any of these commercial topographicmapping systems can be used in the present invention. Typically, ten totwenty tings are projected onto the cornea 600. But up to now thismethod could not be used to extract the true elevation of cornealpoints. The concentric ring method yields information only on the slopeof the cornea between two points. A preferred method for determining X,Y, Z coordinates of corneal points involves a measurement of theelevation of each point not only derivation of elevation informationbased on two-dimensional dam. One of the commercially available systemsfor accomplishing this captures a two-dimensional image of the cornealsurface on video tape. The two-dimensional image of the cornea isdigitized, each pixel of the in, age having a set of X, Y coordinatesand a "brightness" value e.g. , between 0 and 256. A "brighter" pixelwill have a higher value, which directly correlates with the higherelevation (not merely the slope) of the corresponding point on thecornea. The X and Y axes are centered about the optical centerline ofthe patient's eye (which, incidentally, is not necessarily coextensivewith the geometric centerline of the cornea) when the image of thecornea 600 is captured.

The X-Y data representing the two dimensional image of the cornea 600are passed, via data line 612, to a Elevation Analysis Program 620. Ifthe Corneal Image Capture System 610 and Elevation Analysis Program 620are constructed as an integral unit, then data line 612 can take theform of an internal data bus. Alternatively, the X-Y and "brightness"data can be stored in a common area of memory (not shown in FIG. 6)which is accessible to both the Corneal Image Capture System 610 and theElevation Analysis Program 620.

The Elevation Analysis Program 620 is preferably a software programexecuted by a processor. The processor can be custom-designed or canalso be an IBM™ compatible PC. The Program 620 uses an algorithm togenerate a third dimension element, a Z coordinate, for each of the X-Ypairs of data based on the X-Y pair and the brightness of the pixel. Onemethod of calculating the elevation of each point, i.e., the Zcoordinate, is by comparing the X-Y and brightness values measured fromthe patient's cornea 600, to the coordinates and brightness of somereference surface with known elevation, e.g. , a sphere of a knownradius. (The reference values can be pre-stored in Program 620. ) Thefinal output of the Elevation Analysis Program are X-Y-Z coordinates fora multiplicity of points (preferably approximately 1500 or more) on thesurface of the cornea 600. A greater number of X-Y-Z triplets enableseven greater accuracy in the shaping of the contact lens as describedbelow but is not necessary. It will be apparent to those skilled in theart that any method that can generate X, Y, Z corneal data providingboth location and elevation information for points on the cornealsurface with the required accuracy (in this embodiment about 1500 pointsrandomly spaced on the corneal surface) could be used.

The X-Y-Z data output from the Elevation Analysis Program 620 can beformatted in any number of machine-specific ways all well within theskill of the art. In a preferred embodiment of the present invention,the data are formatted in a Data Exchange File format (DXF). The DXFformat is an industry standard format which is typically used for theinter-application transfer of data. The DXF file is a ASCII data filewhich can be read by most of the commonly used Computer Aided DesignSystems 630. The Computer Aided Design System 630 is used in the presentmanufacturing process in order to graphically present to the user (theattending physician or lens manufacturer) the topography of the cornea,and therefore the topography of the custom fit lens which is to beshaped to match the corneal topography. The Computer Aided Design System630 also allows the user to edit the data and to generate newthree-dimensional surfaces (e.g., a spherical surface as describedbelow) derived from the actual corneal surface.

The routing of the X-Y-Z data from the Elevation Analysis Program 620depends on the type of lens to be manufactured and the type of lensblank used as the starting material for the shaping process. If the lensto be manufactured is a fully contoured lens, shaped to conform to thecornea along the entire posterior surface, such as depicted in FIGS. 2and 3, then the X-Y-Z data from the Elevation Analysis Program 620 canbe passed directly to the Command Processor 640 without the need formodification or editing by the Computer Aided Design System 630. Forshaping the anterior lens surface, the posterior lens surface data canbe edited by System 630 to yield an anterior surface with the requisiteeyelid interaction and optical correction, based on methods known in theart.

If the lens to be manufactured is a combination spherical and asymmetricaspheric lens as depicted in FIGS. 4 and 5, the X-Y-Z data contained inthe DXF file from the Elevation Analysis Program 620 has to be editedand/or modified by the Computer Aided Design System 630. The DXF filepassed to the Computer Aided Design System 630 contains data describingthe entire surface of the cornea. If a spherical lens blank is used, theblank needs to be shaped to match the cornea only in the peripheralregion (69 in FIGS. 4 and 5) which will be in contact with the corneaand, optionally, to conform to the cornea in an intermediate zone (101'in FIG. 8). Therefore, any data describing the topography of the corneacorresponding to the central spherical portion of the lens (66 in FIGS.4 and 5) may be disregarded.

As stated previously, the base curve and the width of peripheral portion69 of the lens can determined by the attending physician using theelevation and location of the apex of the cornea and the elevation andlocation of the highest and lowest points on the cornea within the areaunderlying the peripheral area 69. With the aid of the Computer AidedDesign System 630 the base curve and its position are easily calculated.The base curve and position thus calculated can be optionally verifiedby the attending physician or manufacturing specialist before a lensblank with the calculated base curve is actually selected. In theembodiment described here, using a lens blank with the spherical basecurve at the proper height, the Computer Aided Design System 630 willgenerate a DXF file which describes only the peripheral (asymmetric,aspherical) portion of the posterior lens surface between the base ofthe spherical portion and the base of the lens. Note that the peripheralportion of the anterior surface of this lens does not need to bereshaped based on vision correction considerations because theperipheral area of the contact lens is out of the optical field of thecornea. However, as stated above, reshaping of the peripheral portion ofthe anterior lens surface may be required to optimize lens/eyelidinteractions,tear exchange and tear flow. The thus modified DXF file isthen passed onto the Command Processor 640 for generating the commandswhich will actually guide the tool that will shape the lens in theperipheral portion.

It will be apparent to those skilled in the art that further editing ofthe X-Y-Z data may be required, e.g., for such variations as theembodiment of FIG. 8 to provide the "central zone" which bears apredetermined proportionally divergent relationship to the shape of thecorresponding portion of the cornea. The relationship is determinedbased on the tear flow pattern through the cornea that is desired,taking into account the surface tension of the anterior lens surface andof the corneal surface as well as the viscosity of the lacrimal fluidand the capillary nature of the passage between the peripheral portionof the lens and the cornea.

An important advantage of the embodiment using a spherical lens blank isthat the manufacturing cost and time of producing a custom fit contactlens is substantially decreased without sacrifice in comfort or visualacuity. The manufacturing facility is able to stock a variety ofspherical lens blanks which have been pre-fabricated using lessexpensive techniques such as molding or spin casting. When a custom lensis ordered, the manufacturer merely has to select from its inventory alens blank with the proper (e.g. spherical) base curve and optical lenspower or powers required. It must be noted that the methods in thisdescription relating the shaping of contact lenses also apply theshaping of molds which can be used to produce many other lenses.

An alterative embodiment for manufacturing a lens with a combinationspherical central portion and asymmetric aspheric peripheral portiondoes not start with a spherical lens blank. In this embodiment, the basecurve of the central spherical portion of the lens is determined (eitherby the attending physician or by the operator of the Computer AidedDesign System 630) and the Computer Aided Design System 630 is employedto generate X-Y-Z data describing the topography of the sphericalcentral portion. In this embodiment, the Computer Aided Design System630 will generate a DXF file describing the entire surface, bothposterior and anterior surfaces, of the lens which is then passed ontothe Command Processor 640. In this manner both the anterior andposterior surfaces of the lens are shaped, pursuant to the informationfrom the Command Processor including the central spherical portion. Anadvantage to this process is the ability to accommodate a cornea with anon-standard base curve, e.g. , for a patient with a keratoconus.

The Command Processor 640 accepts DXF files containing X-Y-Z datadescribing the surface of the lens to be shaped, and generates asequence of commands which controls the Shaping System 650. The CommandProcessor 640 will take the raw X-Y-Z data from either the ElevationAnalysis Program 620 or the Computer Aided Design System 630 and use theraw data to generate the control signals required to control LensShaping System 650 which then shapes lens blanks. The Command Processor640 is adapted to Lens Shaping System 650 and both units are generallyavailable from the manufacturers of the Lens Shaping System 650. Onecombination of Command Processor and Lens Shaping System is commerciallyavailable as the DLM Series II Micro Mill from DAC of Carpinteria,Calif. Systems incorporating both the Corneal Image Capture System 610and the Elevation Analysis Program 620 are commercially available fromcompanies such as Computed Anatomy (New York, N.Y.), EyeSys Technologies(Houston, Tex.), or PAR Technologies (New Hartford N.Y.) sold undertrademarks or model numbers TMS1, Corneal Analysis System III (CAS III),and Corneal Topography System (CTS) respectively.

Computer Aided Design Systems such as 630 are commercially availableunder the tradenames AutoCAD™, AutoMILL™ and AutoSURF™ from Autodesk ofSausalito Calif. and CADKEY™ from Cadkey Inc., Manchester, Conn.

In a preferred embodiment of the present invention, the Lens ShapingSystem 650 is a three-centerline rotary encoded mill capable of movementin the X, Y and Z axes but other systems having the ability to shapelens blanks asymmetrically in three dimensions with a smooth transition(i.e., without sharp angles) could be used instead. Traditional lathingtechniques are not adequate for this purpose because they do not havethe accuracy or precision of an encoded miller. In addition, some lasertechniques that ablate material from a lens blank may create pits on thelens surface and are therefor also not adequate. However, a conventionallathe may be used to form the spherical central portion.

Lens Shaping System 650 employing a milling tool or "miller" is depictedin FIG. 7. The milling system 650' rests on a stable work table 700(preferably constructed from granite for stability). The surface plate710 is mounted upon vibration isolator 720. A collet 730 for holding thelens blank is mounted on top of the surface plate 710. The surface plate730 acts as an X-Y table, providing motion in the X and Y directions. Zaxis operation is accomplished by vertical spindle 760. Vertical supportframe 740 provides support for the spindle controls 750 and spindle 760.A milling tool 770 is shown mounted in the chuck of the spindle 760. Thesurface plate X-Y motion and the spindle Z direction motion is driven bycrossed roller type bearings and ball screw feeds (not shown). Rotaryencoders (not shown) are typically used to provide high resolutionaccuracy. The controller and associated electronics for the MillingSystem 650' is not shown in FIG. 7.

In operation, the lens blank which is to be milled is held in collet730. Preferably, the lens blank is held in the collet by means of avacuum system (not shown). The series of commands for controlling theX-Y motion of the X-Y table 710 and the Z motion of the spindle 760 arereceived from the Command Processor 640 (FIG. 6). As stated previously,the Command Processor 640 is adapted to the particular milling system650'. The commands are formatted and properly sequenced for use by themill controller. The mill controller generates the actual controlsignals which drive the X-Y notion of the surface plate 710 and the Zaxis motion of the spindle 760. The System 650' allows verticaltranslation of the Z axis in coordination with the movement of the X-Ytable 710. Contrary to a conventional lathing system, in which theworkpiece is rotated, the lens blank on the milling system 650' remainsstationary with respect to the X-Y table 710 and the Z centerlinespindle 760. Since the lens blank remains stationary, thethree-centerline milling system 650 is able to control the X, Y and Zmotion of the milling tool 770 relative to the lens blank and therebycreate a contact lens having at its posterior surface an asymmetricaspheric peripheral portion (or, alternatively, an entire posteriorsurface) that is asymmetric and aspherical and either matches thecorneal surface for which it is custom designed or conforms to thecorneal surface according to a predetermined relationship. In thepreferred embodiment of the milling process, the milling tool willtravel in a composite fashion consisting of a translational componentand a circumferential component over the stirface of the lens to bemilled. The resulting spiral motion will provide a smooth and blendedcurvature of the surface of the lens. The circumferential millingprocess is known as "climb". Any milling process will inherently createridges in the surface of the material being milled. If the ridges are ashigh as 3μ (hill to valley) they create discomfort. Applicant hasdiscovered that by milling the lens in a circumferential manner, asopposed to a radial manner (known as "raster"), the height of the ridgescan be greatly reduced (preferably to less than 2μ and most preferablyto 1μ hill-to-valley). In fact, the height of the ridges are negligible,which Applicant believes is partly due to the fact that the radial stepof the miller between circumferential cuts is preferably very small(i.e., between 0.1 mm and 0.000001 mm). For those embodiments callingfor shaping all or part of the anterior lens surface, analogous shapingoperations will also be performed on that surface based on the teachingsprovided herein.

Although traditional lenses are necessarily circular in shape (becauseof the rotational cutting), no such limitation exists using the shapingtechniques and data of the present invention. For this reason, virtuallyany shape lens can be milled, including an oval (ellipsoidal) shapedlens. The variety of lens shapes enabled by use of the present inventionallow practitioners to develop new approaches to solving the lens/eyelidinteraction problem. The interaction of the eyelid with a contact lenshas traditionally been a problem with contact lenses. As the eyelidcloses, it tends to impact the edge of the lens and displace the lensfrom its centered position. By using a lens shape other than circular,such as an oval shape, the force of the eyelid will be distributed alonga longer edge of the contact lens and therefore the lens will have lessof a tendency to be displaced. Alternatively, if an oval shaped lens isused, the wider diameter of the oval can be oriented along the verticalmeridian of the cornea (i.e., from twelve o'clock to 6 o'clock).Although this orientation will expose the narrowest portion of the lensto the initial contact with the eyelid (which is believed to concentratethe forces from the eyelid to a narrow portion of the lens) the narrowportion will also be supported by the greatest amount of bearingsurface. It is anticipated that a noncircular lens design will assist inalleviating, if not preventing, the lens from being dislodged by theaction of the eyelid.

The asymmetric aspheric posterior surface or surface portion of thecontact lens of the present invention, which matches the asymmetricaspheric contour of the cornea, enables the lens to sit much moresecurely on the cornea and rotate less with respect to the cornea, thanany lens of the prior art. This advantage of the present invention hasseveral aspects. First, as described above, the eyelid tends to displacethe lens when the wearer blinks. Because the lens of the presentinvention has a secure seat on the cornea, this displacement is muchless likely. Even if the lens does become displaced, surface tensionforces will cause it to resume its proper placement (i.e., "centered"position) much more quickly and accurately than any lens of the priorart. Symmetric aspheric lenses of the prior art require a ballast or"weight", usually an additional mass of lens material, in the inferiorquadrant of the lens (the six o'clock position of the lens) in order toproperly orient the lens on the cornea. By the force of gravity, whenthe patient is upright, the heavier part of the prior art lens tends torotate to the inferior quadrant of the cornea. In the lens of thepresent invention, the custom asymmetric contour of the lens will causethe lens to stay centered on the cornea, without the need for a ballastto orient the lens through the operation of gravity. The matchedcontours of the lens and cornea acts as a "key" to properly center thelens on the cornea.

A further advantage of the self aligning or self-centering aspect of thelens of the present invention occurs in the application of bi- ormultifocal lenses. There are two types of such lenses in the prior art:in the first, the portion of the bi-or multifocal lens that is of ahigher power than the rest of the lens is found in the inferiorquadrant. In the second type, the central portion of the bi- ormultifocal lens is set for distance and the power progressivelyincreases in a radial direction. In order to orient the lens of thefirst type properly, the practice in the prior art is to place a ballastin the inferior quadrant to allow gravity to orient the lens. As statedabove, if the patient is in an inclined position (e.g. reading in bed),the effect of gravity upon the lens is misdirected and the lens has atendency to rotate and float away from its aligned position. The secondtype of bifocal or multifocal lens requires no ballast but provides asmaller central field of vision. The first type of bifocal or multifocallens is preferred in the present invention. Since the lens of thepresent invention does not need a ballast for alignment, the wearer canassume any position without the lens becoming displaced or rotate fromits aligned position. Furthermore, if the bi- or multifocal lens of theinvention does become displaced, the lens, floating on the tear filmwill quickly self align in its proper position on the cornea.

The present invention encompasses soft, hard or gas-permeable contactlenses made without limitation from a variety of commercially availablematerials, such as hydrophilic polymers (e.g., hydrogels), poly(methylmethacrylate), or rigid gas-permeable polymeric materials such asfluoro-silicone acrylate (Polymer Technology), flexible fluoro polymers(e.g., A-FPP from Ocular Sciences), siloxane acrylate (CooperVision),stryisilicone (Ocutec), 1-butyl styrene/silicone acrylate (PBH),polysulfone-fluoro silicone acrylate (Progressive Optical Research) andfluoropolymer (American Hydron) which are preferred.

Having thus described a preferred embodiment of the present invention,it is to be understood that the above described device and method ismerely illustrative of the principles of the present invention, and thatother devices may be devised by those skilled in the art withoutdeparting from the spirit and scope of the invention as claimed below.

I claim:
 1. A contact lens for use on a patient's eye with an asymmetricaspheric cornea, said lens having: an anterior surface, a posteriorsurface and a base, said posterior surface comprising a peripheralportion, which is asymmetric and aspherical and at least coextensivewith the base of said lens, said base comprising an edge of variablethickness;said peripheral portion asymmetrically and asphericallymatching a corresponding peripheral portion of the cornea which liesunder said peripheral portion of the lens when the lens is worn in thepatient's eye; and said contact lens having a diameter that is less thanor substantially equal to a diameter of said cornea.
 2. The lens ofclaim 1 wherein said peripheral portion is coextensive with the base ofsaid lens.
 3. The lens of claim 1 wherein said peripheral portion has awidth up to about 1.5 mm.
 4. The lens of claim 1 wherein said peripheralportion has a width up to about 1 mm.
 5. The lens of claim 1 whereinsaid posterior surface further comprises a central portion that isspherical.
 6. The lens of claim 5 wherein at least a portion of saidanterior surface is asymmetric and aspherical and bears a predeterminedrelationship to said posterior surface, said relationship having beendetermined by taking into account the optical correction to be achievedby said lens.
 7. The lens of claim 5 wherein said anterior surface has acentral portion and at least the central portion of said anteriorsurface is spherical.
 8. The lens of claim 1 wherein said base isnon-circular.
 9. The contact lens according to claim 1 wherein said lensis at most about 10 millimeters in base diameter.
 10. The contact lensof claim 1 wherein said lens has superior and inferior quadrants, saidlens further comprising:a portion of said inferior quadrant of said lenshas a power different from the power of said superior quadrant.
 11. Thecontact lens of claim 10 wherein said portion of said inferior quadrantof said lens has a plurality of different powers.
 12. The lens of claim1 wherein the posterior surface of said lens further comprises a centralportion and an intermediate zone between said central portion and saidperipheral portion, said intermediate zone being asymmetric andaspherical, said intermediate zone asymmetrically and asphericallyconforming to a corresponding intermediate zone of said cornea,according to a predetermined proportionally divergent relationship,thereby providing progressively increasing spacing between said lens andsaid cornea along the width of said intermediate zone from saidperipheral portion to said central portion.
 13. The lens of claim 12wherein said peripheral portion has a width up to about 1 mm.
 14. Thelens of claim 12 wherein said central portion is spherical.
 15. Acontact lens for use with an asymmetric aspherical cornea, said lenshaving:an anterior surface, a posterior surface and a base, saidposterior surface comprising a peripheral portion, which is asymmetricand aspherical and at least coextensive with the base of said lens, saidbase comprising an edge of variable thickness; at least said peripheralportion asymmetrically and aspherically matching a corresponding portionof the cornea; and said contact lens having a diameter that is less thanor substantially equal to a diameter of said cornea.
 16. The lens ofclaim 15 wherein the posterior surface further comprises a centralportion, said central portion being no more than about 7 millimeters inbase diameter.
 17. A contact lens having a base, first and secondmeridians, a geometric center, and anterior and posterior surfaces, saidsurfaces each having a central portion and a peripheral portion, saidposterior surface peripheral portion being at least coextensive with thebase, said contact lens comprising, said base comprising an edge ofvariable thickness:said central portion of each of said posterior andanterior surfaces being spherical, said central portion of said anteriorsurface having an apex; a first point on said peripheral portion of saidposterior surface, said first point lying along said first meridian apredetermined radial distance from said geometric center of said contactlens; a second point on said peripheral portion of said posteriorsurface, said second point lying along said second meridian at the samepredetermined radial distance from said geometric center of said contactlens; and said first and second points are at different distances from aplane tangent said lens at said apex.
 18. A method for making a contactlens having a posterior surface comprising a central portion and aperipheral portion comprising the steps of:generating three-dimensionaltopographic data, including elevation data, for a multiplicity of pointson a corneal surface to be fitted with said contact lens, said dataproviding information on both asphericity and asymmetry of said cornealsurface; generating a lens-shaping file based on said data, and on theoptical correction to be achieved by said lens; using said lens-shapingfile to shape a lens blank to produce a contact lens having a posteriorsurface, said posterior surface comprising a peripheral portion which isasymmetric and aspherical and at least coextensive with the base of saidlens, said base comprising an edge of variable thickness; saidperipheral portion asymmetrically and aspherically matching acorresponding peripheral portion of the cornea which lies under acorresponding peripheral portion of the lens when the lens is placed inits worn position in the patient's eye; and said contact lens having adiameter that is less than or substantially equal to a diameter of saidcornea.
 19. The method of claim 18 wherein said peripheral portionextends from the base of said peripheral portion to the base curve ofsaid central portion.
 20. The method of claim 18, said lens furtherhaving an intermediate zone between said peripheral portion and the basecurve of said central portion said intermediate zone conformingaccording to a predetermined proportionally divergent relationship tothe three-dimensional shape of an intermediate corneal surface portionthat underlies said intermediate zone when the lens is worn on saidcornea.